With "Seven Psychopaths," writer-director Martin McDonagh ("In Bruges") serves up a shaggy dog story, in both the literal and figurative senses, which gets exponentially more entertaining as it rolls along.

Colin Farrell meta-fictionally stars as a hard-drinking Irish screenwriter named Martin, who's having a hard time getting started on his new project, a screenplay entitled "Seven Psychopaths." His best pal Billy Bickle (Sam Rockwell, and, yes, note the surname) tries to help out when he's not engaged in a dognapping racket with his partner Hans Kieslowski (Christopher Walken). After Billy and Hans snatch the shih tzu belonging to violent gangster Charlie Costello (Woody Harrelson), Martin gets swept up in the action.

The movie seems to be partially about McDonagh's conflicted attitude about the violence and clichés of just the sort of smart-alecky macho action flick he's made, and partially about giving opportunities to some of the greatest scene-stealing male actors going. Apart from Rockwell, whose manic lunkheadedness can carry huge chunks of time, and Walken, whose deadpan menace can emerge from the most mundane lines, there are brief appearances from Harry Dean Stanton (as "the Quaker psychopath") and Tom Waits (as a rabbit-clutching weirdo).

Consistently surprising, "Seven Psychopaths" ultimately plays like a combination of Quentin Tarantino's self-aware, savvy ultraviolence and Charlie Kaufman's reflexive head trips. And that potentially awkward combo goes down like a chocolate-vanilla swirl cone, only with more guns.